It is often required to disintegrate solids in liquids without incorporating air in certain processes for air could induce undesirable oxidation of the resulting solid-liquid slurry and/or induce foaming. An example is the disintegration of soybeans in water in order to make soymilk. In U.S. Pat. No. 4,915,972 Apr. 10, 1990 Gupta, such disintegration process is described in connection with production of soymilk.
The disintegration of solids in liquids is often achieved by high speed rotating hammermills. However, prior art hammermills create extreme vortex in liquids which induces suction of air in the comminuting region. A hammermill also requires very high starting torque if the solids are already in the mill when it is started. The drive motor has to be sized to provide the required high starting torque, which is expensive and inefficient for running operation. In addition, it yields solid particles of large variation in size which often requires two or more mills in tandem to get reasonable grind of the solids. Alternately, the slurry has to be recirculated many times through the same hammermill. Either approach results in increased capital cost and reduced energy efficiency. U.S. Pat. Nos. 2,738,930 and 2,738,931 May 20,1956 Schneider teach dispersion apparatus in which a preliminary comminuting system is followed by a plurality of dispersion systems. U.S. Pat. No. 2,519,198 Aug. 15,1950 Richeson describes a coffee grinding or comminuting machines having a plurality of rotating cutting elements. U.S. Pat. No. 3,993,791 Nov. 23, 1976 Breed et al is directed to a continuous lautering apparatus in which a series of continuously decanting centrifuges and an equal number of reslurry stations are provided.
The present invention eliminates these deficiencies of a hammermill and provides a highly cost-effective method of grinding for general purpose such as dry grinding of grains, spices, minerals, and other food and non-food products. It is also is suitable for grinding solid in liquids such as ordinary, choked, flooded, and airless grinding. This is achieved by locating the hammering elements only in the vicinity of the impacting surface rather than using the whole rotating element as hammer. The starting and running torque requirement of the drive motor is greatly reduced and energy use efficiency is improved. The motor torque requirement and energy efficiency is further improved by dividing the milling regions into two or more sections. This division also results in good control on the particle size distribution of the grind and eliminates the need for multiple mills or multiple passes to achieve a good grind.